DESCRIPTION

This document is all you need to know about what's required in your package.json
file. It must be actual JSON, not just a JavaScript object literal.

A lot of the behavior described in this document is affected by the config
settings described in npm-config(7).

name

The most important things in your package.json are the name and version fields.
Those are actually required, and your package won't install without
them. The name and version together form an identifier that is assumed
to be completely unique. Changes to the package should come along with
changes to the version.

The name is what your thing is called.

Some rules:

The name must be less than or equal to 214 characters. This includes the scope for
scoped packages.

The name can't start with a dot or an underscore.

New packages must not have uppercase letters in the name.

The name ends up being part of a URL, an argument on the command line, and a
folder name. Therefore, the name can't contain any non-URL-safe characters.

Some tips:

Don't use the same name as a core Node module.

Don't put "js" or "node" in the name. It's assumed that it's js, since you're
writing a package.json file, and you can specify the engine using the "engines"
field. (See below.)

The name will probably be passed as an argument to require(), so it should
be something short, but also reasonably descriptive.

You may want to check the npm registry to see if there's something by that name
already, before you get too attached to it. https://www.npmjs.com/

A name can be optionally prefixed by a scope, e.g. @myorg/mypackage. See
npm-scope(7) for more detail.

version

The most important things in your package.json are the name and version fields.
Those are actually required, and your package won't install without
them. The name and version together form an identifier that is assumed
to be completely unique. Changes to the package should come along with
changes to the version.

Version must be parseable by
node-semver, which is bundled
with npm as a dependency. (npm install semver to use it yourself.)

Or you can shorten that all into a single string, and npm will parse it for you:

"Barney Rubble <b@rubble.com> (http://barnyrubble.tumblr.com/)"

Both email and url are optional either way.

npm also sets a top-level "maintainers" field with your npm user info.

files

The "files" field is an array of files to include in your project. If
you name a folder in the array, then it will also include the files
inside that folder. (Unless they would be ignored by another rule.)

You can also provide a ".npmignore" file in the root of your package or
in subdirectories, which will keep files from being included, even
if they would be picked up by the files array. The .npmignore file
works just like a .gitignore.

main

The main field is a module ID that is the primary entry point to your program.
That is, if your package is named foo, and a user installs it, and then does
require("foo"), then your main module's exports object will be returned.

This should be a module ID relative to the root of your package folder.

For most modules, it makes the most sense to have a main script and often not
much else.

bin

A lot of packages have one or more executable files that they'd like to
install into the PATH. npm makes this pretty easy (in fact, it uses this
feature to install the "npm" executable.)

To use this, supply a bin field in your package.json which is a map of
command name to local file name. On install, npm will symlink that file into
prefix/bin for global installs, or ./node_modules/.bin/ for local
installs.

For example, myapp could have this:

{ "bin" : { "myapp" : "./cli.js" } }

So, when you install myapp, it'll create a symlink from the cli.js script to
/usr/local/bin/myapp.

If you have a single executable, and its name should be the name
of the package, then you can just supply it as a string. For example:

directories

The CommonJS Packages spec details a
few ways that you can indicate the structure of your package using a directories
object. If you look at npm's package.json,
you'll see that it has directories for doc, lib, and man.

In the future, this information may be used in other creative ways.

directories.lib

Tell people where the bulk of your library is. Nothing special is done
with the lib folder in any way, but it's useful meta info.

directories.bin

If you specify a bin directory in directories.bin, all the files in
that folder will be added.

Because of the way the bin directive works, specifying both a
bin path and setting directories.bin is an error. If you want to
specify individual files, use bin, and for all the files in an
existing bin directory, use directories.bin.

directories.man

A folder that is full of man pages. Sugar to generate a "man" array by
walking the folder.

directories.doc

Put markdown files in here. Eventually, these will be displayed nicely,
maybe, someday.

directories.example

Put example scripts in here. Someday, it might be exposed in some clever way.

directories.test

Put your tests in here. It is currently not exposed, but it might be in the
future.

repository

Specify the place where your code lives. This is helpful for people who
want to contribute. If the git repo is on GitHub, then the npm docs
command will be able to find you.

The URL should be a publicly available (perhaps read-only) url that can be handed
directly to a VCS program without any modification. It should not be a url to an
html project page that you put in your browser. It's for computers.

For GitHub, GitHub gist, Bitbucket, or GitLab repositories you can use the same
shortcut syntax you use for npm install:

scripts

The "scripts" property is a dictionary containing script commands that are run
at various times in the lifecycle of your package. The key is the lifecycle
event, and the value is the command to run at that point.

dependencies

Dependencies are specified in a simple object that maps a package name to a
version range. The version range is a string which has one or more
space-separated descriptors. Dependencies can also be identified with a
tarball or git URL.

Please do not put test harnesses or transpilers in your
dependencies object. See devDependencies, below.

Local Paths

As of version 2.0.0 you can provide a path to a local directory that contains a
package. Local paths can be saved using npm install -S or
npm install --save, using any of these forms:

../foo/bar
~/foo/bar
./foo/bar
/foo/bar

in which case they will be normalized to a relative path and added to your
package.json. For example:

{
"name": "baz",
"dependencies": {
"bar": "file:../foo/bar"
}
}

This feature is helpful for local offline development and creating
tests that require npm installing where you don't want to hit an
external server, but should not be used when publishing packages
to the public registry.

devDependencies

If someone is planning on downloading and using your module in their
program, then they probably don't want or need to download and build
the external test or documentation framework that you use.

In this case, it's best to map these additional items in a devDependencies
object.

These things will be installed when doing npm link or npm install
from the root of a package, and can be managed like any other npm
configuration param. See npm-config(7) for more on the topic.

For build steps that are not platform-specific, such as compiling
CoffeeScript or other languages to JavaScript, use the prepare
script to do this, and make the required package a devDependency.

The prepare script will be run before publishing, so that users
can consume the functionality without requiring them to compile it
themselves. In dev mode (ie, locally running npm install), it'll
run this script as well, so that you can test it easily.

peerDependencies

In some cases, you want to express the compatibility of your package with a
host tool or library, while not necessarily doing a require of this host.
This is usually referred to as a plugin. Notably, your module may be exposing
a specific interface, expected and specified by the host documentation.

This ensures your package tea-latte can be installed along with the second
major version of the host package tea only. npm install tea-latte could
possibly yield the following dependency graph:

├── tea-latte@1.3.5
└── tea@2.2.0

NOTE: npm versions 1 and 2 will automatically install peerDependencies if
they are not explicitly depended upon higher in the dependency tree. In the
next major version of npm (npm@3), this will no longer be the case. You will
receive a warning that the peerDependency is not installed instead. The
behavior in npms 1 & 2 was frequently confusing and could easily put you into
dependency hell, a situation that npm is designed to avoid as much as possible.

Trying to install another plugin with a conflicting requirement will cause an
error. For this reason, make sure your plugin requirement is as broad as
possible, and not to lock it down to specific patch versions.

Assuming the host complies with semver, only changes in
the host package's major version will break your plugin. Thus, if you've worked
with every 1.x version of the host package, use "^1.0" or "1.x" to express
this. If you depend on features introduced in 1.5.2, use ">= 1.5.2 < 2".

bundledDependencies

This defines an array of package names that will be bundled when publishing
the package.

In cases where you need to preserve npm packages locally or have them
available through a single file download, you can bundle the packages in a
tarball file by specifying the package names in the bundledDependencies
array and executing npm pack.

we can obtain awesome-web-framework-1.0.0.tgz file by running npm pack.
This file contains the dependencies renderized and super-streams which
can be installed in a new project by executing npm install
awesome-web-framework-1.0.0.tgz.

If this is spelled "bundleDependencies", then that is also honored.

optionalDependencies

If a dependency can be used, but you would like npm to proceed if it cannot be
found or fails to install, then you may put it in the optionalDependencies
object. This is a map of package name to version or url, just like the
dependencies object. The difference is that build failures do not cause
installation to fail.

It is still your program's responsibility to handle the lack of the
dependency. For example, something like this:

Entries in optionalDependencies will override entries of the same name in
dependencies, so it's usually best to only put in one place.

engines

You can specify the version of node that your stuff works on:

{ "engines" : { "node" : ">=0.10.3 <0.12" } }

And, like with dependencies, if you don't specify the version (or if you
specify "*" as the version), then any version of node will do.

If you specify an "engines" field, then npm will require that "node" be
somewhere on that list. If "engines" is omitted, then npm will just assume
that it works on node.

You can also use the "engines" field to specify which versions of npm
are capable of properly installing your program. For example:

{ "engines" : { "npm" : "~1.0.20" } }

Unless the user has set the engine-strict config flag, this
field is advisory only will produce warnings when your package is installed as a dependency.

engineStrict

This feature was removed in npm 3.0.0

Prior to npm 3.0.0, this feature was used to treat this package as if the
user had set engine-strict. It is no longer used.

os

You can specify which operating systems your
module will run on:

"os" : [ "darwin", "linux" ]

You can also blacklist instead of whitelist operating systems,
just prepend the blacklisted os with a '!':

"os" : [ "!win32" ]

The host operating system is determined by process.platform

It is allowed to both blacklist, and whitelist, although there isn't any
good reason to do this.

cpu

If your code only runs on certain cpu architectures,
you can specify which ones.

"cpu" : [ "x64", "ia32" ]

Like the os option, you can also blacklist architectures:

"cpu" : [ "!arm", "!mips" ]

The host architecture is determined by process.arch

preferGlobal

If your package is primarily a command-line application that should be
installed globally, then set this value to true to provide a warning
if it is installed locally.

It doesn't actually prevent users from installing it locally, but it
does help prevent some confusion if it doesn't work as expected.

private

If you set "private": true in your package.json, then npm will refuse
to publish it.

This is a way to prevent accidental publication of private repositories. If
you would like to ensure that a given package is only ever published to a
specific registry (for example, an internal registry), then use the
publishConfig dictionary described below to override the registry config
param at publish-time.

publishConfig

This is a set of config values that will be used at publish-time. It's
especially handy if you want to set the tag, registry or access, so that
you can ensure that a given package is not tagged with "latest", published
to the global public registry or that a scoped module is private by default.

Any config values can be overridden, but of course only "tag", "registry" and
"access" probably matter for the purposes of publishing.

See npm-config(7) to see the list of config options that can be
overridden.

DEFAULT VALUES

npm will default some values based on package contents.

"scripts": {"start": "node server.js"}

If there is a server.js file in the root of your package, then npm
will default the start command to node server.js.

"scripts":{"install": "node-gyp rebuild"}

If there is a binding.gyp file in the root of your package and you have not defined an install or preinstall script, npm will
default the install command to compile using node-gyp.

"contributors": [...]

If there is an AUTHORS file in the root of your package, npm will
treat each line as a Name <email> (url) format, where email and url
are optional. Lines which start with a # or are blank, will be
ignored.